Alternating-current machinery.



PATENTED JAN. 9, 1906.

A. s. MoALLlSTERf ALTERNATING CURRENT MACHINERY.

APPLICATION FILED MAR.2,1905.

W wwwzfla M WW a AM M WW Q 0 @900 Zwf/ 0 X. if 2 UNITED STATES PATENT @FFIOE.

ALTERNATlNG-CURRENT MACHINERY.

Specification of Letters Patent.

Patented Jan. 9. 1906.

Application filed March 2, 1905- Serial NC 248,087-

To all whmn it may concern.-

Be it known that I, ADDAMs STRA'rToN Mc- ALLIsTER, a citizen of the United States, residing'at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Alternating- Ourrent Machinery, of which the following is a specification.

My invention relates to alternating-current machines provided with commutators such as'used in direct-current machines; and its object is to improve the power factor of such machines and to enable the same to be controlled.

By the application of my invention I am enabled to operate alternating-current machines at unity power factor and, if desired, to cause such machines to take a leading current.

The alternating current is particularly adapted to long distance and interurban railway systems on account of the ease With which high voltages may be obtained and the facility of making transformations from one voltage to another; but such systems have not been extensively used up to the present time on account of the difliculties encountered in the motor equipment. While several types of motors have been tried with more or less success, their operation entailed heavy losses in the transmission system and rendered the generator and engine regulation unsatisfactory by reason of the large lagging currents taken by the motors and the consequent lowpower factor of the system.

It is the purpose of my invention to overcome the defects referred to by producing a motor which is particularly adapted for traction-work and Whose power factor may be controlled and maintained at unity, or, if desired, the motor may be made to take leading current.

While my invention may be applied to different types of motors, I have chosen to illustrate it particularly in connection with the compensated series type, so named on account of the character of the field-winding, which is arranged to neutralize or compensate for the armature reaction,

My invention will be best understood by reference to the accompanying drawings, in which Figure l is a diagrammatic representation of a compensated series motor; Fig. 2, of an induction series motor, and Fig. 3 a vector diagram explanatory of the motor represented in Fig. l. 4

In Figs. 1 and 2, A represents the armature, which may be of the ring, drum, or other well-known type and is provided with a commutator similar in general mechanical construction to a direct-current railway-motor armature provided with brushes B B. F is the field-winding, disposed at substantially ninety degrees from the line of the brushes, while the compensating winding 0 is in line therewith and serves to neutralize or compensate for the armature reaction in the manner well known. These coils or windings F and C may be concentrated and, if desired, placed upon projecting pole-pieces or may constitute distributed windings and be disposed in slots or holes in an-annular laminated iron field similar to that of an inductionmotor.

In Fig. 1 the armature, field, and compensating windings are connected to the mainline conductors L L in series relation. In Fig. 2 the line conductors are only connected to the motor-brushes, while the field and compensating windings are connected in closed circuit in a manner clearly described in my former patent, No. 770,091.

Both the compensated series motor and my induction series motor have characteristics similar to the direct-current series motor as to speed and torque, and are therefore especially well fitted for traction-work; but neither of these can be operated at a power factor of unity, though they may be so designed as to have power factors relatively high throughout their range of operation.

Since the power factor directly affects the required capacity and cost of the generating and distributing systems and a high-power factor especially effects a material improvement in the regulation of the alternating-current generators, the production of a motor adapted to traction-work and which at the same time will operate at unity power factor becomes exceedingly important. I have found that I can control the power factor of alterhating-current motors such as described by placing a non-inductive resistance in shunt across the field-winding, as shown at R in the drawings, the value of said resistance being capable of adjustment. The effect of such resistance will be apparent from the following considerations: Assume, first, ideal conditions in which the armature and compensating coils are Without resistance and the compensation is complete, so that these two circuits, treated as one, are withoutinductance. The field-coil is without resistance, but constitutes the reactive portion of the motor-circuits. When the armature is stationary, if the circuit through the resistance R is open the current taken by the machine has a value determined by the ratio of the impressed electromotive force and the reactance of the field-coil. This current lags ninety time-degrees behind the electromotive force across the field-coil. Now if the resistanceR is placed in shunt to the field-coil current flows therethrough quite independently of the field-current. The current taken by the resistance is in time phase with the electromotive force impressed upon the field-coil. An ammeter placed in the fieldcircuit shows the same currentflowing through the field-winding whether the resistance R is connected in shunt thereto or is disconnected.

Referring now to Fig. 3, showing the operation of a compensated series motor in vector diagram, in which all lines are referred to the direction of the field-current, as indicated by the arrow, let OG L- represent the field-current, assumed to be of unit value; OH Ei, the electromotive force impressed across the field-coil F and the shunted resist ance R; GM L, the current taken by the ohmic resistance R; OM I, the current which flows through the armature and compensating coil or the resultant current taken by the motor. This current has a value represented by the equation 1 2 11' I1-2 and has a phase displacement b with reference to the field-current such that tan. Vith unit value of field-current under speed conditions the electromotive force ES HK, countergenerated at the brushes, due to the presence of the field-flux, will be proportional directly to the speed and in time phase with the field-current. Thus this component of the counter electromotive force of the motor is in no wise affected by the presence of the current through the shunted resistance. At a certain speed the countergenerated armature electromotive force will have a value represented by the line HK, the resultant electromotive force OK E being the vector sum of the speed electromotive force E5 and the stationary electromotive force lip-that is E Ef E5 and has a time-phase position a with reference show that under operating conditions the angle of time-phase displacement between the value represented by the equation fl-a, that is, the current leads the electromotive force by the angle At a certain critical speed for each value of the shunted resistance R or at a certain value of said resistance for any given speed the angle reduces to Zero and the power factor of the motor becomes unity. It is thus possible to adjust the resistance so that the motor will operate either at unity power factor or will take a leading current from the line conductors.

It is interesting to observe the effect of removing the resistance from in shunt with the field-circuit. Since the current taken by the resistance is ninety time-degrees from the field-flux, the resultant torque due to the product of this component of the current and the flux is of zero value, the instantaneous torque alternating at double the circuit frequency. The current through the resistance therefore contributes in no way to the power of the machine or to the countergenerated armature-speed electromotive force, and when the circuit through the resistance is opened no effect whatsoever is produced upon the value of the current taken by the field-coil, the counter electromotive force, or the torque of the machine. It is apparent, therefore, that the use of the shunting resistance increases the circuit-current in a certain definite proportion, the added component being a leading wattless current under speed conditions. If, on the other hand, a reactance be placed in parallel with the field-coil, the current which flows therethrough will be in time phase with the field-flux and the torque produced thereby will add to the torque due to the field-current, and it will affect directly the whole performance of the machine. The current taken by a condensance in shunt with the field-coil will be in time-phase opposition to the field-current and will tend to decrease directly both the circuit-current and the armature torque. An excess of condensance will cause the torque to reverse and the machine to act as a generator even when the speed is in a positive direction. \Vhen the condensance and the field reactance are just equal, the circuit-current reduces to Zero and the torque disappears. Under the conditions here assumed the countergenerated electron'iotive force at the armature remains proportional to the product of the field-flux and the speed, and there appears the remarkable combination of zero-current being transmitted over a certain counter electromotive force (that is, through infinite impedance) to divide into definite active currents at the end of the transmission-circuits. This is evident from the fact that when the condensance in shunt equals the inductance of the field-coil the combined circuits will be in resonance and a negligible external current 1 serves to maintain the current in the lield and shunt circuits.

current and the electromotive force 6) has a I This negligible current is transmitted over the counter electromotive force at the armature, and hence, apparently, Z I I 00 I infinite value of the counter electromotive force at the armature impedance. ES is determined by the speed and the field-flux and the latter is determined by and also determines the value of the current in the resonant circuit.

From what has been demonstrated above it is seen that shunted condensance acts to take current in phase opposition and to decrease the torque, reactance takes current directly in phase and increases the torque, while resistance takes current in leading quadratures with the field-current and has no effect upon the torque. It is evident that the improvement in power factor due to the use of the resistance is advantageous provided the losses caused by the resistance are not excessive.

Referring to Fig. 3, when the resistance is not used the power P taken by the machine under speed conditions is P I OGr. OK cos. KOG I If E cos. a, I Ir Es.

When the machine is stationary, the power P, absorbed by the resistance is -Pr GM.OH IrEf- V hen the motor is running with shunted fieldcoil, the power Pt delivered to the machine is Pt I OM OK cos. MOK I I E cos.

cos. (9 I cos. fl cos. a sin. sin. (1/.

Pt I I cos. fl E cos. a I sin. E sin. a. Pt IrESd-IIEr P+PY.

The significance of the last equation is that the energy absorbed is that incident to the use of the resistance and that for a given current it is unaffected by the speed electromotive force. Thus the current taken by the resistance multiplies into the stationary transformer electromotive force to give the actual watts absorbed, while the same current multiplies into the speed electromotive force to give apparent leadin'g wattless power.

In the derivation of the above equations ideal conditions have been assumed; but these cannot be obtained in actual practice, since the windings necessarily have some resistance and the nullification of armature reaction may not be perfect. Accordingly in an actual motor tested it was found that the lines OH and GM, representing, respectively, the field electromotive force Ei. or starting electromotive force and the resistance-current L, were inclined slightly to the right of the vertical and that the speed electromotive force Es rose slightly above the horizontal; but even with an unfavorable machine the power factor was maintained at unity for any speed greater than about one-half synchronism.

In Fig. 2 I have shown how my invention may be applied to the induction series motor, while its application to other types will be clear to those familiar with electrical machinery.

I do not wish to be restricted, therefore, to the particular construction and arrangement of parts herein shown, since changes therein which do not depart from the spirit of my invention and which are within the scope of the appended claims will be obvious to those skilled in the art.

Having thus fully described my invention, I claim as new and desire to protect by Letters Patent of the United States- 1. The combination of an alternating-current machine, having a rotor provided with a commutator means for nullifying the rotor magnetism, and means for maintaining a predetermined power factor at different speeds.

2. The combination of an alternating-current machine, having a rotor provided with a commutator, a field-winding, a compensating winding adapted to nullify the rotor magnetism, and means for controlling the power factor of said machine at difierent speeds.

3. The combination of an alternating-current machine, having a rotor provided with a commutator, a field-winding, a compensating winding adapted to nullify the rotor magnetism, and adjustable means for causing said machine to take current either in phase or leading with respect to the line electromotive force.

I. The combination of an alternating-curent machine, having a rotor provided with a commutator, a stator provided with field and compensating windings, and means connected with a stator-winding for maintaining a predetermined power factor at different speeds.

5. The combination of an alternating-current machine, having a rotor provided with a commutator, a field-winding, and a compensating winding adapted to nullify the rotor magnetism, and a non-inductive resistance in shunt to said lield-winding, and adapted to maintain the power factor at unity.

6. The combination of an alternating-current machine, having a rotorprovided with a commutator, a field-winding, and a compensating winding adapted to nullify the rotor magnetism, and an adjustable non-inductive resistance in shunt to said field-winding, and adapted to maintain the power factor at unity.

7. The combination of an alternating-current machine having a rotor provided with a commutator, a field-winding, and a non-inductive resistance in shunt to said field-winding, and adapted to improve the power factor.

8. The combination of an alternating-current machine having a rotor provided with a commutator, a field-winding, and an adjustable non-inductive resistance in shunt to said rent machine having field and armature members connected in series, a compensating winding adapted to nullify the rotor magnetism, and means for superposing a current in the armature-circuit in quadrature to the working current.

In testimony whereof I afiix my signature in presence of two Witnesses.

ADDAMS STRATTON MOALLISTER.

Witnesses:

HENRY W. BLAKE, THOS. R. TATTAVALL. 

